1. Field of Invention
This invention relates to an evaporation method and a manufacturing method of display device, especially to an evaporation method and an manufacturing method of display device that prevent a mechanical damage to the surface of a substrate, on which a pattern is formed through evaporation.
2. Description of the Related Art
An EL display device with an electroluminescenct (referred to as EL hereinafter) element has been gathering attention as a display device substituting a CRT or an LCD. Development efforts for the EL display device with a thin film transistor (referred to as TFT hereinafter) as a switching device for driving the EL device have been made accordingly.
FIG. 8 is a plan view showing the vicinity of a display pixel of an organic EL display device. FIG. 9A shows a cross-sectional view of the device along the A—A cross-sectional line, and FIG. 9B shows a cross-sectional view of the device along the B—B cross-sectional line in FIG. 8.
As seen from FIGS. 8, 9A, and 9B, the display pixel 115 is formed in an area surrounded with a gate signal line 51 and a drain signal line 52. The display pixels are disposed as a matrix configuration.
An organic EL device 60, which is a light-emitting device, a switching TFT 30 for controlling the timing of supplying electric current to the organic EL device 60, a driving TFT 40 for supplying electric current to the organic EL device 60, and a storage capacitance element are disposed in the display pixel 115. The organic EL device 60 includes an emissive layer consisting of an anode 61, which is a first electrode, and a light-emitting material and a cathode 63, which is a second electrode.
The first TFT 30, which is the switching TFT, is disposed near the crossing of the signal lines 51, 52. A source 33s of the TFT 30 functions also as a capacitance electrode 55 that forms capacitance with a storage capacitance electrode line 54, and is connected to a gate 41 of the second TFT 40, which is an EL device driving TFT. A source 43s of the second TFT is connected to the anode 61 of the organic EL device 60 and a drain 43d is connected to a diving source line 53 that is the source of the electricity supplied to the organic EL device 60.
The storage capacitance electrode line 54 is disposed in parallel with the gate signal line 51. The storage capacitance electrode line 54 is made of chrome and forms capacitance by accumulating electric charge with the capacitance electrode 55 connected to the source 33s of the TFT through a gate insulating film 12. A storage capacitance element 56 is disposed to store the voltage applied to a gate electrode 41 of the second TFT 40.
The TFTs 30,40 and the organic EL device are sequentially disposed on a substrate 10, which may be a glass substrate, a resin substrate, a conductive substrate or a semiconductor substrate, as shown FIGS. 9A and 9B. When the conductive substrate or the semiconductor substrate is used as the substrate 10, an insulating film made of SiO2 or SiN should be disposed on the substrate first. Then the first and second TFTs and the organic EL device are formed. Both TFTs 30,40 should have a top-gate configuration, where the gate electrode is located above an active layer with the gate insulating film between them.
The explanation on the first TFT 30, the switching TFT will be made hereinafter.
As shown in FIG. 9A, an amorphous silicon film (referred to as a-Si film hereinafter) is formed through a CVD method on the insulating substrate 10, which is made of a quartz glass or a non-alkaline glass. The laser beam is shed on the a-Si film for re-crystallization from melt, forming a poly-crystalline silicon film (referred to as a p-Si film, hereinafter). This functions as the active layer 33. Single layer or multiple layers of SiO2 film and SiN film is formed on the p-Si film as the insulating film 12, on which the gate signal line 51 also working as the gate electrode 31 made of a metal with a high-melting point such as Cr, Mo and the drain signal line 52 made of Al are disposed. The driving source line 53 made of Al that is the source of the driving power of the organic EL device is also disposed.
A SiO2 film, a SiN film and a SiO2 film are sequentially disposed to form an interlayer insulating film 15 on the entire surface of the gate insulating film 32 and the active layer 33. A drain electrode 36, which is formed by filling a contact hole formed corresponding to the drain 33d with a metal such as Al, is disposed, and a flattening insulating film 17 made of organic resin for flattening the surface is formed on the entire surface.
Next, the description on the second TFT 40, which is the TFT for driving the organic EL device, will be provided. As shown in FIG. 9B, an active layer 43, which is formed by illuminating the laser beam for poly-crystallization, a gate insulating film 12, and a gate electrode 41 made of a metal with a high-melting point such as Cr, Mo are sequentially disposed on the insulating substrate 10, which is made of a quartz glass or a non-alkaline glass. A channel 43c, and a source 43s and a drain 43d located both sides of the channel 43c are formed in the active layer 43. A SiO2 film, a SiN film and a SiO2 film are sequentially disposed to form the interlayer insulating film 15 on the entire surface of the gate insulating film 12 and the active layer 43. The driving source line 53, which is connected to the driving source by filling a contact hole formed corresponding to the drain 43d with a metal such as Al, is disposed. Furthermore, the flattening insulating film 17 made of organic resin for flattening the surface is formed on the entire surface. A contact hole corresponding to the location of the source 43s is formed in the flattening film 17. A transparent electrode made of ITO that is the anode 61 of the organic EL device making a contact with the source 43s through the contact hole is formed on the flattening film 17. The anode 61 is formed separately, forming an island for each of the display pixel.
The organic EL device 60 has the configuration, where the anode 61 made of the transparent electrode such as ITO (Indium Tin Oxide), a hole transportation layer 62 including a first hole transportation layer made of MTDATA (4, 4-bis (3-methylphenylphenylamino) biphenyl) and a second hole transportation layer made of TPD (4, 4, 4-tris (3-methylphenylphenylamino) triphenylanine), an emissive layer 63 made of Bebq2 (bis(10-hydroxybenzo[h]quinolinato)beryllium) including quinacridone derivative, an electron transportation layer 64 made of Bebq2, and the cathode 65 made of either magnesium-indium alloy, aluminum, or aluminum alloy are disposed in this order.
In the organic El device 60, a hole injected from the anode 61 and an electron injected from the cathode 65 are recombined in the emissive layer and an exciton is formed by exciting an organic module forming the emissive layer 63. Light is emitted from the emissive layer 63 in a process of relaxation of the exciton and then released outside after going through the transparent anode 61 to the transparent insulating substrate 10, thereby to complete light-emission.
This technology is described in, for example, Japanese Laid-Open Patent Publication No. H 11-283182.
The organic EL material used in the hole transportation layer 62, the emissive layer 63, and the electron transportation layer 64 of the organic EL device 60 has a low anti-solvent property and it is vulnerable to water. Therefore, the photolithographic technology of the semiconductor process can not be utilized. Thus, the hole transportation layer 62, the emissive layer 63, and the electron transportation layer 64 of the organic EL device 60 are formed by evaporation using a shadow mask.
Next, the pattern forming method through evaporation of the organic EL material will be explained by referring to FIGS. 10-13. The reference numeral 100 indicates the vacuum evaporation device, the reference numeral 101 an exhaust system, the reference numeral 110 a supporting table in the chamber of the vacuum evaporation device 100. A shadow mask (an evaporation mask) 111 made of magnetic material such as nickel (Ni) or invar alloy (Fe64,Ni36) is disposed on the supporting table 110. A plurality of opening portions 112 is formed in the predetermined locations of the shadow mask 111.
A magnet 120, which is movable in vertical direction, is disposed on the shadow mask 111 on the supporting table 110. The reference numeral 130 indicates a glass substrate known as a mother glass between the magnet 120 and the shadow mask 111. The reference numeral 140 denotes a evaporation source located underneath the shadow mask 111 and movable in the horizontal direction along with the shadow mask 111.
Suppose the chamber of the vacuum evaporation device 100 is kept vacuum by the exhaust system 101, in FIG. 10. The glass substrate 130 is inserted between the magnet 120 and the shadow mask 111 by a transportation system not shown in the figure. Then the glass substrate 130 is disposed on the shadow mask 111 by the transportation system as seen from FIG. 11.
Then, the magnet 120 is moved downwards to touch the upper surface of the glass substrate 130 as shown in FIG. 12. The shadow mask 111, receiving magnetic power from the magnet 120, is tightly placed to the lower surface of the glass substrate 130, on which a pattern will be formed.
The evaporation source 140 is moved in the horizontal direction from the left edge to the right edge of the glass substrate 130, as seen from FIG. 13, by a moving system not shown in the figure. During the evaporation source 140 is moving, the organic EL material is evaporated and deposited to the surface of the glass substrate 130 through the opening portion 112 of the shadow mask 111. The evaporation source 140 is a crucible tall in the vertical direction, as shown in FIG. 13. The evaporation material in the crucible is heated by a heater for evaporation.
The magnet 120 moves upwards when the evaporation is finished. The glass substrate 130 is lifted from the shadow mask 111 and moved to the location of the next operation by the transportation system. This completes the pattern forming of the organic EL device 60.
However, the conventional evaporation method described above has a problem of giving a mechanical damage to the pattern forming surface of the glass substrate 130, damaging the organic EL device.
This problem is caused by a friction between the shadow mask 111 and the glass substrate 130, giving a mechanical damage to the surface of the glass substrate 130, when (1) the shadow mask 111 is disposed on the glass substrate 130 by the transportation system, (2) the glass substrate 130 is tightly placed to the shadow mask 111 by the magnet 120, and (3) the shadow mask 111 is lifted from the glass substrate 130.
The size of the glass substrate 130 has been becoming larger in recent years. Therefore, the deformation of the glass substrate 130 becomes bigger during the processes of (1) and (3) described above, and bigger damages result when the deformed area of the glass substrate 130 touches the surface of the shadow mask 111.